Xanthus Pharmaceuticals, Inc. presented data demonstrating that SymadexTM, a
selective FLT3 inhibitor, acted to reverse disease in mouse models of both acute
and chronic multiple sclerosis. Biomarkers of macrophage and dendritic cells
showed a significant correction back towards the baseline levels found in
healthy control animals. The results were presented in a poster session by
Stephen J. Karlik, Ph.D., Professor of Diagnostic Radiology at the University of
Western Ontario, London, Ontario, together with researchers from Xanthus at the
60th American Academy of Neurology Meeting in Chicago, IL.

Using the
experimental autoimmune encephalomyelitis (EAE) model, the effect of Symadex was
evaluated during both the acute and chronic phases of EAE in the mouse models. A
partial, concentration-dependant decrease in clinical signs was observed in the
acute prevention experiment, and chronic treatment resulted in a dose-dependent
reduction of clinical scores. Plasma titers in a combined treatment group versus
disease controls showed significant changes with a trend towards restoring
baseline levels of biomarkers found in naïve controls. Symadex has previously
shown therapeutic benefit in both the acute and chronic stages of the guinea pig
EAE model as well as a similar effect on innate cell biomarkers.

"This
study adds to the growing body of work supporting the ability of Symadex to
potentially prevent and reverse chronic disease in animal models of multiple
sclerosis," said Dr. Karlik. "The evidence that Symadex targets innate immune
cell function in the treatment of MS is encouraging and is a foundation for the
Company's continued work on Symadex in autoimmune models."

About
Symadex™

Symadex (formerly C-1311) is the lead compound in clinical
development from a new series of agents, the imidazoacridinones, which have
shown in vitro to be potent and selective FLT3 receptor tyrosine kinase
inhibitors. Xanthus is exploring the use of Symadex and follow-on compounds for
the treatment of a number of autoimmune diseases, such as multiple sclerosis and
inflammatory bowel disease. Early preclinical data has shown encouraging signs
of activity in models of autoimmune disease. Given the compound's safety profile
and oral availability, Xanthus believes Symadex represents an exciting drug
opportunity.

About Xanthus Pharmaceuticals, Inc.

Xanthus
Pharmaceuticals, Inc. is developing a portfolio of novel, clinical-stage,
small-molecule therapeutic candidates through a management team whose
accomplished track record encompasses all aspects of drug development, from
discovery through regulatory approval and commercialization. The Company is
applying its expertise to advance its current pipeline to address significant
unmet medical need in oncology and autoimmune diseases.

Xanthus is
headquartered in Cambridge, Massachusetts with an additional facility in
Montreal, Quebec. More information is available at http://www.xanthus.com.

This press release contains
forward-looking statements concerning Xanthus that involve a number of risks and
uncertainties. For this purpose, any statements contained herein that are not
statements of historical fact may be deemed to be forward-looking statements.
Without limiting the foregoing, the words, "believes," "anticipates," "plans,"
"expects," "estimates," "intends," "should," "could," "will," "may," and similar
expressions are intended to identify forward-looking statements. There are a
number of important factors that could cause Xanthus' actual results to differ
materially from those indicated by such forward-looking statements, including
risks as to whether results obtained in early clinical studies or in preclinical
studies such as the studies referred to above will be indicative of results
obtained in future clinical trials or warrant additional trials; whether
products based on Xanthus' technology will advance through the clinical trial
process and receive approval from the United States Food and Drug Administration
or equivalent foreign regulatory agencies; whether the company will have the
cash resources to develop and commercialize its products; and whether the patent
and patent applications owned or licensed by Xanthus will protect the Company's
technology and prevent others from infringing it. Xanthus disclaims any
intention or obligation to update any forward-looking statements.